Coupling for electrical oscillation-circuits.



R. H. RENDAHL.

COUPLING FOR ELECTRICAL OSCILLATION CIRCUITS.

APPLICATION FILED SEPT. 7. 1911.

Patnted Mar. 14, 1916.

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MANY,

COUPLING FOR ELECTRICAL OSCILLATIDN-CIRC'UITS.

Speeificationof Letters Patent. I Pafl g mtgfl Maui, 14 1%16,

Application filed September 7, 1911. Serial No. 6482M.

To all whom it may concern Be it known that l, RAGNAR ll-linen REN-DAHL, a subject of the King of Sweden, and residing at Liljeholmen, nearStockholm, Sweden, have invented certain new and use ful Improvements inCouplings for Electrical Oscillation-Circuits, of which the following isa specification.

This invention has for its object an arrangement for connecting anelectric oscillation circuit with apparatus which may consistsubstantially of an ohmic resistance or which will actas such, 6. g.apparatus such as wire instruments, microphones and I cuit to theapparatus, also is accompanied by a variation in the periodicity of theoscillation-circuit.

In receiver circuit arrangements for wireless telegraphy and telephony,it is frequently necessary to vary the energy transmitted from theaerial to the detector, or in other words, to vary the coupling betweenthe aerial and the detector circuit, or also which amounts to the sameto more or less dampen a receiver circuit through the detector.

Various means have been employed heretofore to obtain this result asWell in socalled direct or conductive connections as also in inductiveconnections between the antenna circuit and the receiver circuit. Allthese means, however (some of which are for instance the varying of theeffective turns of a coupling coil or also shifting of the twotransformer coils relatively to each other), have" the result that thereceiver circuit varies its own periodicity, because when the couplingis varied, the inductance of this circuit is varied with it. Thereforeit has always been necessary heretofore to retune the circuit by meansof the tuning device of the antennae. Applicant has now found by existsin all coupling arrangements heretofore employed for this purpose.

It is the object of the present invention to avoid all the disadvantagespointed out 1 above, and also to arrange the coupling of the detectorcircuitso that the means by which the coupling is brought about do nothave any undesirable influence on the oscillation circuit, so that thedampening may be varied at will by means of the detector withoutrequiring a subsequent retuning. This is attained by the combination ofa detector which constitutes a pure ohmic resistance, with a transformerwhich has practi-' cally no magnetic stray flux. Both of these elementsare known in themselves in the art of wireless telegraphy and have beenfrequently used alone or in combination with other elements but so faras I am aware they I have never been used together in a receivercircuit. Transformers with small stray flux have been used for instanceby Marconi (see, 1

Marconi Patent No. 627,650). but only in arrangements in which a cohererwas used as a receiving instrument, which device, as is known,constitutes such a high ohmic resistance so long as notatlected by.Waves, that it acts as a capacity. On the other hand, detectors whichare pure ohmic resistances have been used frequently of late but theyhave only been used in arrangements in which the coupling means have avery large magnetic stray flux.

The effect of using atransformer without stray flux is that thefrequency of the tuned circuit remains constant or approximatelyconstant, even if considerable variations in the coupling and transferofenergy are made. To take tin example: In the methods of couplinghitherto employed,

more particularly by means of transformers extent, may. however, beentirely left out of practical consideration. In consequence of the verysmall stray flux of the transformerits self-induction, so long as theohmic resistance is connected, is extremely low and has therefore noappreciable influence on drawings the oscillationcircuit comes intoaction, and

the increasing of thewave length of this oscillation circuit may nowamount to 30%;

Various forms of construction of the in-.

vention and details of the same are shown diagrammatically Figure 1 isan example of a simple form of construction of the invention, Fig. 2 isa cross section of a coupling transformer; and Figs. 3 and f aredifferent forms of construction of the invention in their application towireless telegraphy. Y In F ig. 1 the oscillation circuit is formed by acondenser C, a self-induction coil L and the primary coil P of atransformer which has substantially no stray flux. An apparatusconsisting of an ohmic resistance such as a detector D, isconnected inseries with the secondary coil P of the transformer.

In order to make it possible to vary the transmissions of energy fromthe oscillation circuit to the apparatus without change in thetransformer ratio, a suitable variable self inductiomfor instance in theform of a variometer V is connected in parallel with one of the .twotransformer coils, for instance as shown, in parallel to theprimary coilP,'. If in an extreme case,;this selfinduction V is 1121, that is to sayif the primary coil P is short-circuited, no transferring of energy tothe detector or ohmic resistance D takes place. The other extreme casearises when V, is opened or is infinitely great. when the detectorreceivesvthe full energy. Owing to the above described arrangement ofthe transformer, a variation of the number of oscillations in theprimary circuit is in practice hardly appreciable, even in these twoextreme cases. Within these two limits the transmission of energy may,of course, be very greatly varied.

Any other suitable alternating current resistance may of course'beemployed instead of the variometer to the same advantage.

In order to obtain the desired very small dispersion in the transformer,it may for instance be wound in a ring form in the 'manner which isalready known for other purposes, as shown in section in Fig. 2. Withsuch a method of winding, in which the primary coil issurrounded on bothsides by the windings of the secondary coil, it is possible to obtain,as is well known, the

greatest mutual induction with the smallest dispersion. The coil mayalso be a continu-. .ousone and the ratio of transformation may beobtained by tappings, z'. e. the coil may constitute anauto-transformer. The advan- 6? tages hereinbefore mentioned only arise,

in the accompanying fore mentioned cannot possibly be obtained. I Theimproved arrangement is therefore only applicable as a receiverarrangement for detectors which substantlally act electrlcally asohmicreslstances. For these, however,

it has extremely important advantages. The

action of the transformer is then as follows:

- When the detector is connected with thesecondary coil itsresistance'must be considered 1 in value equal to its absolute valuedivided by the square of the transformer ratio, and this resulting valueas being directly connected with the primary circuit through thetransformer which is free from dispersion.

If, for instance, theabsolute resistance of the detector amounts to 1000ohms and the ratio of transformation is 10 to 1, the detector resistancewhich' comes into action in the primary circuit is reduced by thetransformer from 1000 ohms to 10 ohms. Efforts find a detector, -theresistance of which is so low that it can be inserted into the primaryoscillation circuit, for instance, the antenna I detectors with such'alow resistance are in- .90 4 have been made in vain for a long time to,

sufficiently sensitive. By the present inven-' tion whatever detector isused its resistance may actas a low resistance detector inserted intothe antenna if a transformer with a suitable ratio of transformation" isused. The reduction of the resistance is preferably such that thedamping caused by the detector is equal to the damping of the primarycircuit at no load." The primary damping will thus generally be doubled-Fig. 3 shows the simplest practical refceiver arrangement according tothis invention. The antenna J is connected to earth through a variometerV and the primary coil P of the transformer, and its V The detector D,and the block con- 11o periodicity 'can bevaried by the variometerdenser B with a telephone T in parallel, are

connected in known manner in the circuit- The coupling may be suitablyvaried by means of the variometer V without affect of the secondary coilP of the transformer.

ing the tuning; In order to increase thefreedom from interruptiontheconnections i may also be extended by the coupling of the detector withthe antenna through a tuned intermediate or selection" circuit (Fig. 4),

which circuit is connected through the coupling transformer K K with theantenna.

The intermediate circuit consists of the secondary coil K a fixedcondenser C, a fixed self-induction coil L,'a variometer V and theprimary coil P out the transformer (without stray flux) connected inparallel with the variometer V .If the capacity C and the self-inductioncoil L in the intermediate circuit are equal to the capacity andself-induction of the antenna, and .if an antenna-variometerds also usedas the vari-.

o-meter in the intermediate circuit, the ad vantage is obtained that thecoupling between the intermediate or selection circuit and the antennae,i. 6. between K and K need not be varied when the wave length is varied,and further the advantage that in working with the selection circuit itsvariometer has always the same adjustments as the variometer of theaerial wire.

Having now particularly described and ascertained the nature of the saidinvention and in what manner the same is to be performed, I declare thatwhat I claim is 2-- 1. In a circuit connection of the characterdescribed, the combination with an oscillation circuit and an electricapparatus substantially constituting a non-inductive ohmic resistance;of a high frequency transformer, having its primary and secondarywinding arranged in suitable close proximity to practically prevent astray flux, the primary winding of said transformer being connected withsaid oscillation circuit and the secondary winding with said apparatus.

2. In a circuit connection of the character described, the combinationwith an oscillation circuit, and an electric apparatus substantiallyconstituting a non-inductive ohmic resistance; of a high frequencytransformer, having its primary and secondary winding arranged insuitable close proximity to practically prevent a stray flux, theprimary winding of said transformer being connected with saidoscillation circuit and the secondary winding with said apparatus, and avariable alternating current resistance connected in parallel with oneof the windings of said transformer.

-3. In a circuit connection of the character described, the combinationwith an oscillation circuit and a circuit containing a detectorconstituting a non-inductive ohmic resistance; of a high frequencytrans-l former having its primary and secondary winding arrangedinsuitable close proximity to practically prevent a stray flux, th primarywinding of said transformer bein connected with said oscillation circuitan the secondary winding being connected with a circuit containing saiddetector.

4. In a circuit connection of the characlation circuit and a circuitcontaining a-detector constituting a non-inductive ohmic resistance andcontaining means for indicating electric oscillations; of ahighfrequency transformer having its primary and secondary windingarranged in suitable close proximity to practically prevent a strayflux, the primary winding of said transformer being connected with saidoscillation circuit and the secondary winding being connected with acircuit containing said detector, and a variable alternating currentresistance connected in parallel with one of the windings of saidtransformer.

5. In a circuit connection of the character described, the combinationwith an oscillation circuit and a circuit containing a detectorconstituting .an ohmic resistance; of a high frequency transformerhaving its primary and secondary winding arranged in suitable closeproximity to practically prevent a stray flux, the primary winding ofsaid transformer being connected with said oscillation circuit. and thesecondary winding being connected with a circuit containing saiddetector, said transformer having a suitable transformation ratio tocause the detector in the detector circuit to substantially double thedamping of the circuit containing the primary winding of thetransformer.

6. In a circuit connection of the character described, the combinationwith an oscillation circuit, a tuned intermediate circuit looselycoupled with said oscillation circuit and a detector circuit containinga detector constituting an ohmic resistance and means for indicatingelectric oscillations; of a high frequency transformerhaving its primaryand secondary winding arranged in suitable close proximity topractically prevent a stray flux, the primary winding of said .windingsof said transformer.

In testimony whereof, I afiix my signature in the presence" of twowitnesses.

RAGNAR HAKAN RENDAHL. Witnesses:

GRETA PRICE, ERNEST L. HARRIS.

